[PATCH] mm: compaction: fix the page state calculation in too_many_isolated

[Vinayak Menon <vinmenon@codeaurora.org>]

Commit "3611badc1baa" (mm: vmscan: fix the page state calculation in
too_many_isolated) fixed an issue where a number of tasks were
blocked in reclaim path for seconds, because of vmstat_diff not being
synced in time. A similar problem can happen in isolate_migratepages_block,
similar calculation is performed. This patch fixes that.

Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>
---
 mm/compaction.c | 32 +++++++++++++++++++++++++++-----
 1 file changed, 27 insertions(+), 5 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 546e571..2d9730d 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -537,21 +537,43 @@ static void acct_isolated(struct zone *zone, struct compact_control *cc)
 	mod_zone_page_state(zone, NR_ISOLATED_FILE, count[1]);
 }
 
-/* Similar to reclaim, but different enough that they don't share logic */
-static bool too_many_isolated(struct zone *zone)
+static bool __too_many_isolated(struct zone *zone, int safe)
 {
 	unsigned long active, inactive, isolated;
 
-	inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
+	if (safe) {
+		inactive = zone_page_state_snapshot(zone, NR_INACTIVE_FILE) +
+			zone_page_state_snapshot(zone, NR_INACTIVE_ANON);
+		active = zone_page_state_snapshot(zone, NR_ACTIVE_FILE) +
+			zone_page_state_snapshot(zone, NR_ACTIVE_ANON);
+		isolated = zone_page_state_snapshot(zone, NR_ISOLATED_FILE) +
+			zone_page_state_snapshot(zone, NR_ISOLATED_ANON);
+	} else {
+		inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
 					zone_page_state(zone, NR_INACTIVE_ANON);
-	active = zone_page_state(zone, NR_ACTIVE_FILE) +
+		active = zone_page_state(zone, NR_ACTIVE_FILE) +
 					zone_page_state(zone, NR_ACTIVE_ANON);
-	isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
+		isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
 					zone_page_state(zone, NR_ISOLATED_ANON);
+	}
 
 	return isolated > (inactive + active) / 2;
 }
 
+/* Similar to reclaim, but different enough that they don't share logic */
+static bool too_many_isolated(struct zone *zone)
+{
+	/*
+	 * __too_many_isolated(safe=0) is fast but inaccurate, because it
+	 * doesn't account for the vm_stat_diff[] counters.  So if it looks
+	 * like too_many_isolated() is about to return true, fall back to the
+	 * slower, more accurate zone_page_state_snapshot().
+	 */
+	if (unlikely(__too_many_isolated(zone, 0)))
+		return __too_many_isolated(zone, 1);
+	return 0;
+}
+
 /**
  * isolate_migratepages_block() - isolate all migrate-able pages within
  *				  a single pageblock
-- 
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